Abstract
Among various climate drivers, direct evidence for the Intertropical Convergence Zone (ITCZ) control of sediment supply on the millennium scale is lacking, and the changes in ITCZ migration demonstrated in paleoclimate records need to be better investigated. Here, we use clay minerals and Sr-Nd isotopes obtained from a gravity core on the Ninetyeast Ridge to track the corresponding source variations and analyze the relationship between terrestrial material supplementation and climatic changes. On the glacial-interglacial scale, chemical weathering weakened during the North Atlantic cold climate periods, and falling sea level hindered the transport of smectite into the study area due to the exposure of islands. However, the influence of the South Asian monsoon on the sediment supply was not obvious on the millennium scale. We suggest that the north-south migration of the ITCZ controlled the rainfall in Myanmar and further directly determined the supply of clay minerals on the millennium scale because the transport of smectite was highly connected with ITCZ location. Furthermore, the regional shift of the ITCZ induced an abnormal increase in the smectite percentage during the late Last Glacial Maximum (LGM) in our records. The smectite percentage in the studied core is similar to distinct ITCZ records in different time periods, revealing that regional changes in the ITCZ were significantly obvious, and that the ITCZ is not a simple N-S displacement and closer connections occurred between the Northern-Southern Hemispheres in the eastern Indian Ocean during the late Last Glacial Maximum (LGM).
Highlights
Deposited sediments are essential recorders of the paleoclimate and paleo-ocean since the climate is tied to the whole sedimentation process, from weathering and transport to the deposition of sediments on land
Kaolinite percentage ranges from 2% to 16%, and chlorite percentage ranges from 5% to 20% in the core sediments
From 35-21 ka, the falling sea level led to an increase in the exposed area of the Andaman-Nicobar Islands and further hindered the entrance of smectite from the Andaman Sea into the study area
Summary
Deposited sediments are essential recorders of the paleoclimate and paleo-ocean since the climate is tied to the whole sedimentation process, from weathering and transport to the deposition of sediments on land. The terrestrial materials of "source-sink" systems are supplied to marine environments under the combined effects of multiple climate-related driving forces and ocean processes (Li et al, 2018; Yu et al, 2019), and understanding these effects is crucial for reconstructing coevolutionary relationship of the paleoenvironment with the paleo-oceans and paleoclimate. Evidence for direct control of terrestrial sediment supply by the ITCZ remains lacking, which is an obstacle to understanding the response of the depositional environment to the ITCZ shift. The paleoclimate breakthroughs mentioned above enable us to analyze the response of sedimentary records to the ITCZ shift in the BoB more accurately
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